Without limiting the scope of the invention, its background is described in connection with medical implants.
Over the past decade, the number of load-bearing and non-load-bearing or low-load-bearing metal or alloy implants for biomedical applications has increased dramatically, with current estimates in the millions worldwide. These include orthopedic joint implants, rods, bone plates, and varieties of maxillofacial or craniofacial replacements [1,2]. In load-bearing implant cases, in particular, biomechanical mismatch between the implant and the surrounding bone often leads to inhomogeneous stress transfer or so-called stress-shielding phenomena. This often leads to stress concentration by bone remodeling and retarded bone healing [3,4] which can lead to loosening and subsequent revision surgery. Revision surgeries are often more complicated than the original surgery, and most individuals can only undergo a few such surgeries. Mechanical biocompatibilities require strong, light-weight, low modulus of elasticity (or Young's modulus), non-toxic metals or alloys. However, even implants with a low elastic modulus similar to bone may not alleviate loosening because there may be no provision for bone tissue ingrowth. Bone consists of an outer cortical shell with an elastic modulus ranging from 18 to 20 GPa and a density of roughly 1.9 g/cm3, in contrast to the inner (medullary) trabecular bone which is a highly porous, reticulated structure with roughly 55 to 70 percent interconnected porosity (or roughly 1.3 to 2.0 g/cm3 density) [5]. Cell penetration and tissue ingrowth requires an interconnected pore system with pore diameters in excess of 0.1 mm [6,7]. This is especially true for non-load-bearing craniofacial implants. Consequently porous metal implants can provide for tissue ingrowth as well as more homogeneous stress transfer for load-bearing implant applications based upon model predictions for open cellular materials by Gibson and Ashby [8]:E=Eo(ρ/ρo)n,  (1)
where, E and Eo are the elastic (Young's) moduli of the cellular (foam) and fully dense material, respectively, ρ and ρo are the corresponding porous and bulk densities, and n has values ranging from 1.8 to 2.2 [9].
Open-cell titanium and titanium alloy structures have been fabricated by a number of solid-state processes: controlled powder sintering (including hollow powder sintering), gas expansion followed by sintering, polymeric foam replication, etc. [10-12]. Cellular lattices, lattice-truss structures or lattice-block structures (three-dimensional-periodic reticulated materials, especially cast Ti-6Al-4V lattice-block structures) have recently been described by Li, et al. [14], while Heinl, et al. [15] have described cellular Ti-6Al-4V structures for bone implants fabricated by selective electron beam melting.
United States Patent Application No. 20070151961 (Kleine and Gale, 2007) disclose methods and systems for laser machining a substrate in the fabrication of an implantable medical device. The Kleine invention relates to laser machining of implantable medical devices such as stents. Laser machining refers to removal of material accomplished through laser and target material interactions. Generally speaking, these processes include laser drilling; laser cutting; and laser grooving, marking, or scribing. Laser machining processes transport photon energy into a target material in the form of thermal energy or photochemical energy. Material is removed by melting and blowing away, or by direct vaporization/ablation.
A method of producing a customized surgical tool, comprising the steps of obtaining image data corresponding to a patient body region, processing the image data to produce fabrication data; and rapid prototyping the customized surgical tool according to the fabrication data is taught in United States Patent Application No. 20090221898 (Hillis, et al., 2009). m\Many technologies may be implemented as the rapid prototyping machine in the Hillis invention, for example, Stereolithography, Fused Deposition Modeling, and/or Electron Beam Melting.
United States Patent Application No. 20090035448 (Flanagan and O'Connor, 2009) describe a method of making a medical device with a porous coating, the method comprising: providing a workpiece sized to fit within lumens of the body, the workpiece having an accessible surface; positioning a nozzle adjacent the accessible surface; ejecting a coating material from the nozzle toward the accessible surface; directing a laser beam toward the coating material ejected from the nozzle, thereby melting the coating material with the laser; allowing the melted coating material to cool and form a porous coating on the workpiece; and loading the porous coating with a therapeutic agent.